Technical Field
Embodiments of the present invention relate to a display apparatus and a driving method thereof, and particularly, to a display apparatus for performing external compensation through a sensing line.
Discussion of the Related Art
A flat panel display (FPD) apparatus may be applied to various electronic devices, such as portable phones, tablet personal computers (PCs), notebook computers, etc. Examples of the FPD apparatus include liquid crystal displays (LCD), plasma display panels (PDPs), organic light emitting diode (OLED) display apparatuses, etc. Recently, electrophoretic displays (EPD) have been more widely used as an FPD apparatus.
Among the displays, organic light emitting displays use a self-emitting device and thus may typically have a fast response time, high emission efficiency, high luminance, and a wide viewing angle.
That is, OLED displays are self-emitting apparatuses that recombine an electron with a hole to emit light from an OLED, thereby displaying an image. OLED displays typically have a fast response time and lower power consumption. Furthermore, because they include a self-emitting device, they typically have a good viewing angle. Therefore, OLED display apparatuses are attracting much attention as a next generation FPD apparatus.
However, in a related art OLED display apparatus, a characteristic deviation of a threshold voltage (Vth) and a mobility of a driving transistor occurs in each pixel due to a process differential, deterioration, and/or the like. Therefore, the amounts of currents for driving a plurality of OLEDs differ, and for this reason, a luminance deviation occurs between pixels.
In order to solve such a problem, an external compensation method that corrects input image data to compensate for a characteristic change of a driving transistor included in each pixel is disclosed in Korean Patent Publication No. 10-2013-0066449 (or U.S. 2013/0147694).
FIG. 1 is an example diagram of a related art OLED display apparatus showing a horizontal line where sensing for external compensation is performed. In FIG. 1, point A refers to one sub-pixel provided on a horizontal line where sensing for external compensation is not performed, and point B refers to one sub-pixel provided on a horizontal line where sensing for external compensation is performed. Also, plot (a) of FIG. 1 shows luminance at point A, and plot (b) of FIG. 1 shows luminance at point B.
In OLED display apparatuses, sensing for external compensation is generally performed in units of one horizontal line, for example, during a vertical blank time provided between frames.
In this case, in a horizontal line where sensing for external compensation is performed, an image is not displayed during the vertical blank time. Therefore, as shown by example in FIG. 1, the horizontal line where the sensing for external compensation is performed is illustrated as a dark line. For example, an image is not displayed on a plurality of sub-pixels provided on the horizontal line where the sensing for external compensation is performed, and thus, the horizontal line has low luminance in comparison with other horizontal lines.
As shown in plot (b) of FIG. 1, a non-emission period (e.g., no emission) when light is not emitted from an OLED occurs in a sub-pixel where sensing for external compensation is performed. In this case, as shown in plot (b) of FIG. 1, the non-emission period when light is not emitted from the OLED includes a period when sensing is performed, and moreover includes a period (a curve period) when an anode is charged with a voltage for emitting light from the OLED after the sensing period.
However, as shown in plot (a) of FIG. 1, a sub-pixel where sensing for external compensation is not performed continuously emits light. Therefore, a luminance of a horizontal line where sensing for external compensation is performed is lower than that of a horizontal line where sensing for external compensation is not performed. The resulting horizontal line where sensing for external compensation is performed may be seen by a user's eyes.
This visible phenomenon, where a horizontal line is seen by a user, may severely occur in a pixel that emits light at a low gray scale. For example, because a pixel that emits light at a low gray scale has a low level of current, an anode charging period of the pixel is extended. Therefore, a non-emission area is enlarged, and for this reason, the visible phenomenon where a horizontal line is seen by a user is intensified. Moreover, an upper end and a lower end of a panel can have a difference in the degree of the visible phenomenon where a horizontal line is seen by a user.
The above-described phenomenon may generally occur in OLED display apparatuses. However, it can also occur in other various kinds of display apparatuses where external compensation is performed.